Together enteric pathogens are responsible for an estimated 2 million deaths annually and cause millions more cases of diarrheal illness annually, even in developed countries. S. typhimurium is one of the most common causes of diarrhea and is transmitted primarily by ingestion of contaminated food. Although the infected individual typically recovers from the abdominal pain and diarrhea, an individual will continue to shed S. typhimurium for up to three months, and in some individuals for up to a year after the initial symptoms. Therefore it is clear the bacteria have the capability of surviving and growing in the host.
Based on annotated whole genome sequences, intestinal disease-causing bacteria such as Salmonella, Escherichia coli, Shigella, Yersinia, and Campylobacter all contain homologous hydrogenases. Hydrogenases are membrane associated “H2 splitting” enzymes, that carry out the following relatively simple H2 oxidizing reaction: H2−=>2e−+2H+. Metal containing hydrogenases are subdivided into three classes: Fe (“iron only”) hydrogenases, Ni—Fe hydrogenases and Ni—Fe—Se hydrogenases. The membrane-bound hydrogenases associated with H2 oxidation typically split molecular H2 via the NiFe metal center, with the release of protons and low potential electrons (see Vignais, et al., (2001) FEMS Microbiol. Rev. 25:455-501).
The Ni—Fe hydrogenases are heterodimeric proteins consisting of small (S) and large (L) subunits. The small subunit contains three iron-sulphur clusters, two [Fe4S4]2+/1+ and one [Fe3S4]1+/0, and the large subunit contains a nickel-iron centre. The hydrogen (H2) splitting reaction by Ni—Fe hydrogenases does not yield energy as ATP per se, but the two protons released from H2 can contribute to a proton gradient across the membrane. Importantly, the NiFe hydrogenase enzymes are membrane associated where the electrons generated from splitting molecular hydrogen are sequentially passed to heme-containing or quinone-reactive proteins. The potential energy thus generated can be used for ATP production via oxidative phosphorylation or to drive carbon transport systems.
Only recently has the process of energy generation from H2 been recognized as being potentially important for bacterial pathogenesis within animal hosts (Olson and Maier (2002) Science. 298:788-1790). Hydrogen is present in animal's digestive tract as a consequence of the fermentive metabolism by the normal colonic flora. Therefore, the possession of hydrogenase enzymes by enteric bacterial strains, together with a readily available source of H2 in the digestive tract, may play an important role in enteric bacteria's ability to proliferate in the digestive tract of an animal.
One aspect of the present disclosure relates to compositions and a method of reducing the virulence of pathogenic bacteria by preventing the expression of functional hydrogenase activity in the bacteria.